Material used for spring connection devices must exhibit the ability to maintain adequate contact pressure for the design life of any part formed from the material. This ability to maintain adequate contact pressure is the ability to resist stress relaxation over a period of time, especially at temperatures elevated above normal room temperature. The current trend in connector design has been to place greater emphasis upon the maintenance of high contact pressure on connector parts at mildly elevated temperatures to anticipate any problems which might develop in use. Alloys 220 and 260 are currently widely used for electrical connectors but tend to exhibit a rather poor stress relaxation resistance at temperatures of 75.degree. C. or higher. Accordingly, it is important that these widely used alloys be modified in such a manner so as to improve their elevated temperature stress relaxation performance.
It is important to any modifications of Alloys 220 and 260 that the conductivity of these alloys be maintained without any detrimental effect upon improvements in the stress relaxation performance. Furthermore, bend formability should be maintained while any cost increase in the alloys should be held down as low as possible to keep such alloys competitive in the market. Other performance characteristics such as stress corrosion, solderability, softening resistance and others should not be significantly degraded below those properties shown by Commercial Alloys 220 and 260. It is desirable in the present invention that the performance of such alloys exhibit approximately a 25% increase over projected stress remaining after 100,000 hours at 75.degree. C. or higher relative to Alloys 220 and 260. It is also desirable in the present invention that such alloys maintain approximately a 25% IACS conductivity while keeping any cost increase determined by the metal value plus conversion cost below 10% greater than the cost of Alloy 260.
One alloy system which has been developed in the prior art is an improved beta-brass alloy as shown in U.S. Pat. No. 4,055,445 to Horace Pops. This particular patent teaches a brass alloy which exhibits a shape memory effect and which may contain from 25 to 40% by weight zinc along with 0.25 to 3.0% by weight silicon. It should be noted that the only useful alloy system within this broad range is shown by the cross hatched area in FIG. 3 of said patent, wherein the alloy should have a minimum amount of 25% by weight beta-phase up to 75%. Apparently, not only the particular alloy system itself but its specific processing is important in preparing the improved alloy of this particular patent. It is quite important to this patent that an annealing be performed so as to provide the above-mentioned minimum amount of beta-phase material within the alloy system.
It is a principal object of the present invention to provide an alloy system which exhibits improved stress relaxation resistance, particularly at elevated temperatures, when compared to Commercial Alloys 220 and 260.
It is a further object of the present invention to provide an alloy system as aforesaid which maintains approximate conductivity values found in Alloys 220 and 260 without detrimentally affecting the improved stress relaxation resistance.
It is an additional object of the present invention to provide an alloy system as aforesaid which either Ffrom a consideration of the following specification.